The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions. In one embodiment, the present invention is related to encapsulated toner compositions comprised of a core and a polymeric shell thereover preferably prepared by interfacial polymerization which shell contains an organosilane moiety derived from certain organosilane components such as a functionalized alkoxysilane, chlorosilane, siloxysilane and the like, which organosilane reagent is capable of reacting with the shell monomers, and undergoing hydrolysis and a condensation reaction. In an embodiment of the present invention there are provided encapsulated toner compositions comprised of a core comprised of a suitable known polymer resin, and dye or pigment particles, which core is encapsulated within a polymeric shell coating such as a polyurea, a polyurethane, a polyamide, a polyester, or mixtures thereof, and wherein the shell has incorporated therein as an integral part of its structure an organosilane moiety derived from a functionalized organosilane enabling a number of advantages for the resulting toner including no agglomeration or minimal agglomeration, and minimized or no image ghosting when such a toner is selected for the development of images. In another embodiment of the present invention, there is provided an encapsulated toner composition comprising a core of an acrylic, methacrylic, styrene polymer resin or their copolymeric derivatives, pigment, and encapsulated thereover a polymeric shell wherein the shell has incorporated therein an organosilane moiety obtained from a functionalized alkoxysilane, a halosilane, a siloxysilane, or mixtures thereof. In a specific embodiment of the present invention, there are provided encapsulated toner compositions comprised of a polymeric shell obtained by interfacial polymerization, which shell has incorporated therein as an integral component of the shell material an organosilane component derived from, for example, a functionalized alkoxysilane, halosilanes such as chlorosilane, siloxysilane and the like, and a core comprised of dyes, pigments or mixtures thereof. Examples of advantages associated with the toner compositions of the present invention in embodiments thereof include the elimination or the minimization of image ghosting, improved toner fixing characteristics, superior release properties enabling their selection, for example, in imaging systems wherein a release fluid such as a silicone oil is avoided, no or minimal toner agglomeration, excellent powder flow characteristics, no or minimal leeching of the core components, and avoidance of core resin component adherence to the imaging components such as, for example, dielectric receivers or photoreceptors. The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ionographic processes. In one embodiment, the toner compositions can be selected for pressure fixing processes wherein the image is fixed with pressure. Pressure fixing is common in ionographic processes in which latent images are generated on a dielectric receiver such as silicon carbide, reference U.S. Pat. No. 4,885,220 entitled Amorphous Silicon Carbide Electroreceptors, the disclosure of which is totally incorporated herein by reference. The latent images can then be toned with a conductive encapsulated toner of the present invention by inductive single component development, and transferred and fixed simultaneously (transfix) in one single step onto paper with pressure. Specifically, the toner compositions of the present invention can be selected for the commercial Delphax printers, such as the Delphax S9000, S6000, S4500, S3000, and Xerox printers such as the 4060.TM. and 4075.TM. wherein, for example, transfixing is utilized. In another embodiment, the toner compositions of the present invention can be utilized in xerographic imaging apparatus wherein image toning and transfer are accomplished electrostatically, and transferred images are fixed in a separate step by means of a pressure roll with or without the assistance of thermal or photochemical energy fusing. Also, the encapsulated toners of the present invention in an embodiment thereof can be selected, it is believed, for magnetic image character image recognition (MICR) processes, reference U.S. Pat. No. 4,517,268 and Reissue 33,172, the disclosures of which are totally incorporated herein by reference, and wherein with such processes image smearing may be avoided or minimized.
The toner compositions of the present invention can, in one specific embodiment, be prepared by first dispersing the toner precursor materials into stabilized microdroplets of controlled droplet size and size distribution, followed by shell formation around the microdroplets via interfacial polymerization, and subsequently generating the core polymer resin within the newly formed microcapsule by addition polymerization, preferably free-radical polymerization within the resultant microcapsules. Thus, in one embodiment, the present invention is directed to a process for the simple, and economical preparation of pressure fixable encapsulated toner compositions by interfacial/free-radical polymerization methods wherein there are selected as the core polymer resin precursors an addition-type monomer or monomers, a colorant including pigments, dyes or mixtures thereof, and shell-forming monomers, wherein at least one of the shell monomers is oil-soluble, and at least one is water-soluble; which monomers are capable of undergoing condensation polymerization at the microdroplet/water interface. The shell precursors in the aqueous phase also include at least one suitably functionalized organosilane reagent such as, for example, a functionalized alkoxysilane capable of undergoing reaction with the oil-soluble shell monomer in the microdroplet phase. Other process embodiments of the present invention relate to, for example, interfacial/free-radical polymerization processes for obtaining encapsulated colored toner compositions. Further, in another process aspect of the present invention the encapsulated toners can be prepared without organic solvents as the diluting vehicle or as a reaction medium, thus eliminating explosion hazards associated therewith; and furthermore, these processes, therefore, do not require expensive and hazardous solvent separation and recovery steps. Moreover, with the aforementioned process of the present invention there is obtained in an embodiment thereof improved product yield per unit volume of reactor size since, for example, the extraneous solvent component can be replaced by liquid core and shell monomers.
Encapsulated and cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of advantages in comparison to toners that are fused by heat, primarily relating to the utilization of less energy since the toner compositions can be fused at room temperature. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions must usually be fixed under high pressure, which has a tendency to severely disrupt the toner fixing characteristics of the toner selected. This can result in images of low resolution, or no images whatsoever. Also, with some of the prior art cold pressure toner compositions substantial image smearing can result from the high pressures selected. The high fixing pressure also generates in some instances glossy images and objectionable paper calendering problem. Additionally, the preparative processes of the prior art pressure fixing toner compositions usually employ organic solvents as the diluting vehicles and reaction media, and this could drastically increase the toner's manufacturing cost because of the expensive solvent separation and recovery procedure, and the necessary precautions that have to be undertaken to prevent the solvent associated hazards. Moreover, the involvement of an organic solvent in the prior art processes also may decrease the product yield per unit volume of reactor size. In addition, the solvents in many prior art processes may have deleterious effects on toner particle morphology and bulk density as a result of their removal from the toner particles during the toner isolation stage, thus causing shrinkage or collapse of the toner particles resulting in a toner of very low bulk density, which disadvantages are substantially eliminated with the process of the present invention in an embodiment thereof. Furthermore, with many of the prior art processes narrow size dispersity toner particles cannot be easily obtained by conventional bulk homogenization techniques as contrasted with the process of the present invention wherein narrow size dispersity toner particles can be obtained. More specifically, thus with the encapsulated toners of the present invention, control of the toner physical properties of both the core and shell materials can be desirably achieved. Specifically, with the encapsulated toners of the present invention undesirable leaching or loss of core components is minimized or avoided, and image ghosting is eliminated, in many instances, primarily in view of the presence in the shell of an organosilane moiety formed from the reaction of functionalized alkoxysilane, chlorosilane, or siloxysilane reagent with the shell monomer or monomers. Image ghosting, which is one of the known common phenomena in ionographic printing processes, refers to, for example, the contamination of dielectric receiver by residual toner materials which cannot be readily removed in the cleaning process. The result is the retention of latent images on the dielectric receiver surface after cleaning, and the subsequent unwarranted development of these images. One of the common causes of image ghosting is related to the leaching of the sticky core polymer resin out to the toner's surface leading to their adherence to the dielectric receiver during the image development process.
In a patentability search report the following United States patents were listed: U.S. Pat. No. 4,514,484 directed to a powder suitable for developing latent images comprising magnetic particles coated with a mixture of a thermoplastic resin and a silane, see for example the Abstract of the Disclosure; note column 3, beginning at line 15, wherein it is indicated that into the organic thermoplastic resin is incorporated a silane selected from those illustrated; also incorporated into the thermoplastic resin are magnetic materials, see column 3, beginning at line 35; U.S. Pat. No. 4,565,773 directed to dry toners surface coated with nonionic siloxane polyoxy alkalene copolymers with a polar end, see the Abstract of the Disclosure; and primarily of background interest is U.S. Pat. No. 4,640,881; 4,740,443; 4,803,144 and 4,097,404, the disclosure of which is totally incorporated herein by reference.
The following prior art, all United States patents, are mentioned: U.S. Pat. No. 4,770,968 directed to polysiloxane butadiene terpolymer toner resins, reference for example column 4, and note the formulas of FIGS. 1 to 6, including FIG. 2B, which toners can be selected wherein silicone release oils are avoided with no apparent teaching in this patent directed to encapsulated toners; U.S. Pat. No. 4,814,253 directed to encapsulated toners comprised of domains containing a polymer component having dispersed therein a release composition and thereover a host resin component comprised of toner resin particles and pigment particles, see for example the Abstract of the Disclosure and column 4, and note column 4 wherein there is illustrated as one of the components of the encapsulated toner domains comprised of styrene butadiene block polymers such as Kraton, styrene copolymers, or styrene siloxanes, which components have entrapped or dissolved therein mineral oils or silicon oils; U.S. Pat. No. 4,430,408 relating to developer compositions containing a fluorene modified alkyl siloxane and a surface treatment carbon black, reference the Abstract of the Disclosure for example; U.S. Pat. No. 4,758,491 relating to dry toner and developer compositions with a multiphase polyorgano siloxane block or graft condensation copolymer, which provides polyorgano siloxane domains of a particular size and concentration at the toner particle surfaces; and U.S. Pat. No. 4,820,604 directed to toner compositions comprised of resin particles, pigment particles, and a sulfur containing organo polysiloxane wax such as those of the formulas illustrated in the Abstract of the Disclosure.
There are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there are disclosed in the prior art encapsulated toner compositions containing in some instances costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Moreover, illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process.
Disclosed in U.S. Pat. No. 5,045,422 entitled Encapsulated Toner Compositions, the disclosure of which is totally incorporated herein by reference, are encapsulated compositions containing cores comprised of a fluorocarbon and a monomer or monomers. More specifically, there is illustrated in the aforementioned Patent an encapsulated toner composition comprised of a core with a fluorocarbon-incorporated resin binder, pigment or dyes, and a polymeric shell; and an encapsulated toner composition comprised of a core comprised of a fluorocarbon-incorporated resin binder derived from the copolymerization of an addition-type monomer and a functionalized fluorocarbon compound represented by Formula (I), wherein A is a structural moiety containing an addition-polymerization functional group; B is a fluorine atom or a structural moiety containing an addition-polymerization functional group; and x is the number of difluoromethylene functions, pigment or dyes, and a polymeric shell. Also, illustrated in U.S. Pat. No. 5,013,630 entitled Encapsulated Toner Compositions, the disclosure of which is totally incorporated herein by reference, is an encapsulated toner composition comprised of a core comprised of pigments or dyes, and a polysiloxaneincorporated core binder resin, which core is encapsulated in a shell. Moreover, illustrated in U.S. Pat. No. 5,023,159, the disclosure of which is totally incorporated herein by reference, are encapsulated toners with a soft core comprised of silane modified polymer resin, a colorant, and a polymeric shell thereover. Specifically, in one embodiment there is disclosed in the aforementioned Patent encapsulated toners comprised of a core containing a silane-modified polymer resin, preferably obtained by free-radical polymerization, silane-modified pigment particles or dyes, and thereover a shell, preferably obtained by interfacial polymerization. The U.S. Pat. No. 5,023,149 in one embodiment is directed to an encapsulated toner composition comprised of a core comprised of the polymer product of a monomer or monomers, and a polyfunctional organosilicon component, and more specifically wherein the core is comprised of a silane-modified polymer resin having incorporated therein an oxysilyl (I), a dioxysilyl (II), or a trioxysilyl (III) function of the following formulas, pigment, dye particles or mixtures thereof; and a polymeric shell. ##STR1##
The aforementioned toners can be prepared by a number of different processes including the interfacial/free-radical polymerization process which comprises (1) mixing or blending of a core monomer or monomers, up to 25 in some embodiments, a functionalized organosilane, a free-radical initiator or initiators, pigment, and a shell monomer or monomers; (2) dispersing the resulting mixture of pigmented organic materials by high shear blending into stabilized microdroplets in an aqueous medium with the assistance of suitable dispersants or emulsifying agents; (3) thereafter subjecting the aforementioned stabilized microdroplets to a shell forming interfacial polycondensation; and (4) subsequently forming the core resin binder by heat-induced free-radical polymerization within the newly formed microcapsules. The shell forming interfacial polycondensation is generally accomplished at ambient temperature, but elevated temperatures may also be employed depending on the nature and functionality of the shell monomer selected. For the core polymer resin forming free-radical polymerization, it is generally effected at a temperature of from ambient temperature to about 100.degree. C., and preferably from ambient or room temperature, about 25.degree. F. temperature to about 85.degree. F. In addition, more than one initiator may be utilized to enhance the polymerization conversion, and to generate the desired molecular weight and molecular weight distribution.
There is a need for encapsulated toner compositions with many of the advantages illustrated herein. More specifically, there is a need for encapsulated toners wherein image ghosting is eliminated or minimized, and wherein the toners enable image transfer efficiencies of from about 90 to about 99 percent in embodiment of the present invention. Also, there is a need for pressure fixable encapsulated toners which provide quality images with acceptable fixing levels, for example over 80 percent at low fixing pressure of, for example, 2,000 psi. Moreover, there is a need for encapsulated toners, including colored toners wherein image ghosting, and the like are avoided or minimized. Additionally, there is a need for encapsulated toners, including colored toners with excellent release characteristics enabling their selection in imaging systems without the use of surface release fluids such as silicone oils to prevent image offsetting to the fixing or fuser roll. Furthermore, there is a need for encapsulated toners, including colored toners with substantially no toner agglomeration, with long shelf life exceeding, for example, 18 months. Also, there is a need for encapsulated toners that have been surface treated with additives such as carbon blacks, graphite or the like to impart to their surface certain conductive characteristics such as providing a volume resistivity of from about 1.times.10.sup.3 ohm-cm to about 1.times.10.sup.8 ohm-cm. Furthermore, there is a need for encapsulated toners wherein surface additives, such as metal salts or metal salts of fatty acids and the like, are utilized to assist in the release of the images from the imaging component to the paper substrate. There is also a need for simple and economic processes for the preparation of encapsulated toners. Specifically, there is a need for interfacial/free-radical polymerization processes for black and colored encapsulated toner compositions comprised of a hard polymeric shell and a core, and wherein organic solvents are eliminated in their preparation in some embodiments. Moreover, there is a need for enhanced flexibility in the design and selection of the shell and core materials for pressure fixable encapsulated toners and/or flexibility controlling the toner physical properties such as the bulk density, particle size, and size dispersity.